Folding bicycles and wheelchairs are well known and include a frame that will fold. However, the wheels used are a fixed size and the size of the wheels limits the size that the bicycle or wheelchair can be folded (the “package size”).
Small wheels have certain disadvantages when the bicycle or wheelchair is being used. Small wheels have higher rolling resistance in contact with the road than larger wheels, meaning that the bicycle or wheelchair is harder to propel and so is slower. There is also more friction from the wheel bearing because a smaller wheel rotates faster for a given speed than a larger wheel. Furthermore, larger diameter wheels are more comfortable than smaller wheels as they can span small dips in the road or pavement, which smaller diameter wheels fall into. In the case of bicycles, smaller diameter wheels generate lower gyroscopic forces than larger wheels, making them less stable to ride. In addition, large wheels are needed on wheelchairs to enable the user to reach the circumferential push rims to propel the wheelchair along.
On the other hand bicycles and wheelchairs with large wheels cannot be folded into such small packages as those with smaller wheels, making them harder to store and more unwieldy to carry and transport.
A variety of folding bicycles are available commercially, having a variety of different wheel sizes to suit individual cyclist's priorities. However, it would be desirable to provide a folding bicycle with larger wheels that can be folded into a smaller-size package. Likewise, it would be desirable to provide a wheelchair with foldable wheels so it can more easily be carried around and fit in the boot (trunk) of a car. This is achieved, in accordance with the present invention, by providing wheels whose configuration and shape can be altered which gives bicycle and wheelchair designers flexibility to design different configurations of folding bicycles and wheelchairs that have large wheels.
U.S. Pat. No. 4,465,321 describes a portable collapsible spokless wheel for rotation within a fender (mudguard). Rollers are distributed around the inner surface of the fender, which extends around over half of the circumference of the wheel. The wheel rotates on the rollers within the fender.
U.S. Pat. No. 4,602,823 describes a collapsible wheel having a rim made of flexibly jointed rim segments and spokes made of fabric material that can be tensioned.
FR-2795947 discloses a wheel for a wheelchair that can be used to climb small steps. The wheel has a rim supported on telescopic spokes, which are biased outwards by springs to maintain the rim in a circular shape in normal use. However, when the wheel encounters the edge of a step, the force due to the contact with the step telescopes some of the spokes, thereby allowing the wheelchair to mount the step. The rolling resistance of such an arrangement is very high and it would be difficult to propel such a wheelchair.
GB-573956 discloses a folding wheel having four wheel rim segments. The joint between adjacent rim segments are supported by spokes, at least three of which must have adjustable lengths; the length of one spoke is adjustable telescopically and the lengths of another two spokes are adjustable by including a folding joint part of the way along the lengths of the spokes. Such an arrangement is complex and heavy.